Circle absorber exhaustion — FRCA Primary MCQ

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ModeratePhysics and Clinical MeasurementCircle absorber exhaustionFRCA Primary

During low-flow anaesthesia with a circle system, inspired CO2 rises and the capnogram baseline no longer returns to zero. What is the most likely equipment explanation?

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Correct answer: E — Exhausted carbon dioxide absorbent

Rebreathing of CO2 in a circle system with an elevated capnograph baseline suggests exhausted absorbent, incompetent valves or inadequate fresh gas flow; exhausted absorbent is the best option here. Pipeline pressure and vaporiser filling do not cause inspired CO2. Arterial line damping and pulse oximetry faults are unrelated monitors. Capnography is more reliable than absorbent colour change for detecting rebreathing.

Reference: Dorsch and Dorsch Understanding Anesthesia Equipment; RCoA Primary FRCA Syllabus